The impact of multi-level interventions on the second-wave SARS-CoV-2 transmission in China

Background A re-emergence of COVID-19 occurred in the northeast of China in early 2021. Different levels of non-pharmaceutical interventions, from mass testing to city-level lockdown, were implemented to contain the transmission of SARS-CoV-2. Our study is aimed to evaluate the impact of multi-level control measures on the second-wave SARS-CoV-2 transmission in the most affected cities in China. Methods Five cities with over 100 reported COVID-19 cases within one month from Dec 2020 to Feb 2021 were included in our analysis. We fitted the exponential growth model to estimate basic reproduction number (R0), and used a Bayesian approach to assess the dynamics of the time-varying reproduction number (Rt). We fitted linear regression lines on Rt estimates for comparing the decline rates of Rt across cities, and the slopes were tested by analysis of covariance. The effect of non-pharmaceutical interventions (NPIs) was quantified by relative Rt reduction and statistically compared by analysis of variance. Results A total of 2,609 COVID-19 cases were analyzed in this study. We estimated that R0 all exceeded 1, with the highest value of 3.63 (1.36, 8.53) in Haerbin and the lowest value of 2.45 (1.44, 3.98) in Shijiazhuang. Downward trends of Rt were found in all cities, and the starting time of Rt < 1 was around the 12th day of the first local COVID-19 cases. Statistical tests on regression slopes of Rt and effect of NPIs both showed no significant difference across five cities (P = 0.126 and 0.157). Conclusion Timely implemented NPIs could control the transmission of SARS-CoV-2 with low-intensity measures for places where population immunity has not been established.

. Daily new COVID-19 infections and moving average curves at city-level..

Confirmed COVID-19 cases
A confirmed COVID-19 case was defined as a person who: i) met two or more clinical criteria (fever with or without respiratory symptoms; radiographic characteristics of COVID-19; laboratory evidence of normal or decreased count of leukocytes and/or lymphopenia in the early stage of the disease), ii) had an epidemiological link to a SARS-CoV-2 positive individual or had been to regions reporting SARS-CoV-2 transmission within 14 days before disease onset (including clustering transmission), iii) had a positive real-time RT-PCR result or the virus genetic sequence matching known strains of SARS-CoV-2.

Asymptomatic SARS-CoV-2 infected individuals
An asymptomatic SARS-CoV-2 infected individual was defined as a person whose upper respiratory specimens tested positive in real-time RT-PCR without any identifiable clinical symptoms or any COVID-19-related CT imaging characteristics.
When showing COVID-19-related signs or symptoms, the asymptomatic cases would be re-diagnosed as confirmed COVID-19 cases within 24 hours.

Classification of SARS-CoV-2 infected individuals
In the analyses, the SARS-CoV-2 infected individuals were categorized into 3 types as the asymptomatic, confirmed cases from general population and confirmed cases from the asymptomatic. The asymptomatic referred to those who had been diagnosed and first reported as asymptomatic cases without considering whether they would later become confirmed cases or not. Confirmed cases from general population referred to those who had been diagnosed and first reported as confirmed cases following the case definitions listed above. Confirmed cases from the asymptomatic referred to those who were diagnosed and first reported as asymptomatic cases and re-diagnosed as confirmed cases later, also known as presymptomatic cases. The daily incremental number of SARS-CoV-2 infected person were only composed of two parts, the asymptomatic and confirmed cases from general population.

Mass testing
This intervention refers to citywide SARS-CoV-2 testing, the date used for visualization is the date when the testing begins to be enforced in the affected city.
To detect the asymptomatic and cut off the transmissions as soon as possible, mass testing is implemented weekly by the municipal Center for Disease Control and Prevention (CDC) in the second wave.

Potential exposed group testing
With the demand of region-specific, multi-level targeted approach to prevent and control epidemic, this policy refers to testing for close contacts of confirmed cases and the asymptomatic, as well as residents in the same and nearby communities.

School closure
This intervention is mainly aimed at the after-school training institutions, while in the case of Shijiazhuang, it refers to all primary and secondary schools offline education suspend since the risk level of affected region has been raised to "High Risk" level.

Home quarantine
It refers to stay at home and separate from others for "14+7" days at the family unit. During the quarantine time, everyone has to take SARS-CoV-2 tests at day 1,7,13 and 20 for COVID-19 case identification.

Within-city traffic restriction
Different from the lockdown, this intervention specially limits the traffic within the city partly or wholly, including taxi, bus and subway.

Environmental sanitization
To minimize the burden of environment associated infection, the governments organize a thorough terminal disinfection across the entire city.

Social distancing
As one of the common interventions against the spread of the COVID-19 epidemic, this measure includes stopping aggregative activities, closing non-essential public places and restricting all other unnecessary contacts.

Lockdown
The intervention is the strictest COVID-19 epidemic control measures which incorporates implementation of closed-end management, closure of assembly occupancies, ordering people to stay at home. In other words, lockdown encompasses all other interventions mentioned above.

Supplementary Note 2. Cumulative confirmed COVID-19 cases before Jan 2, 2021 in Hebei, Jilin and Heilongjiang provinces
To justify the estimates of R0 in the main analyses, we collected data on cumulative confirmed cases in Hebei, Jilin and Heilongjiang provinces before the second wave in mainland China (retrospective data at the prefectural-city level were hard to obtain from official public sources). As shown in Table S1, comparing with the permanent residents, the proportions of cumulative confirmed cases were less than 0.02‰ in all provinces.

Supplementary Note 3. Estimation of time-varying reproduction number
Following Cori [2], the infectiousness profile was assumed to be independent of  Table   S3-S7.